Human Health and Disease
Class 12 · Biology
4 ideas in Class 12 Biology, explained in plain words, with games and quizzes to practise.
Common Infectious Diseases
Part of: Germs Around Us
Typhoid spreads through contaminated food and water and is confirmed by the Widal test; pneumonia and colds ride droplets; malaria needs humans plus mosquitoes with haemozoin causing cyclic chills; amoebiasis, ascariasis, elephantiasis and ringworm each have their own carriers and cures. Hygiene, vector control and vaccines break every route.
Why it matters. Carrier-disease matching plus route reasoning dominates this section.
Formulas
- Typhoid fever runs 39 to 40 degrees
- Colds last 3 to 7 days
- Malaria chills repeat every 3 to 4 days
Key words
- Pathogen
- : An organism causing disease.
- Widal test
- : The typhoid confirmation test.
- Vector
- : A living transmitter of germs.
- Haemozoin
- : The toxin behind malaria chills.
- Sporozoites
- : The infective malaria stage.
- Elephantiasis
- : Limb swelling from filarial worms.
Try it in two minutes
- Pair each pathogen with its carrier.
- Sort diseases by food, air and vector routes.
- Assign one prevention per route.
Try at home. Explain why Gambusia fish join mosquito control.
Body Defences
Part of: Germs Around Us
Innate guards include skin, stomach acid, white cells and interferons, while acquired arms build antibodies and T-cell memory. Active immunity follows infection or vaccines; passive arrives ready-made through colostrum or injections. Allergies overreact with IgE, autoimmunity attacks self, and lymphoid organs train cells.
Why it matters. Active-passive splits plus memory logic answer most immunity questions.
Formulas
- Antibody chains follow H2L2
- MALT forms half the lymphoid tissue
Key words
- Innate immunity
- : Born non-specific defence.
- Acquired immunity
- : Learned pathogen-specific defence.
- Antibody
- : A Y protein neutralising germs.
- Active immunity
- : Defence the body builds itself.
- Passive immunity
- : Ready-made defence received.
- Allergen
- : A substance triggering allergy.
- MALT
- : Lymphoid tissue lining tracts.
Try it in two minutes
- List four innate barriers.
- Split active from passive cases.
- Place B and T cells on a flowchart.
Try at home. Explain why second encounters hit harder.
AIDS and Cancer
Part of: Hard Battles
HIV enters through intimate contact, transfused fluid, shared needles or from mother to child, copies RNA into DNA, and destroys helper T cells until minor germs turn dangerous; ELISA detects it and prevention beats cure. Cancer loses contact inhibition; benign stays put while malignant spreads by metastasis, with tobacco, radiation and viruses as triggers.
Why it matters. Transmission routes plus tumour contrast are exam favourites.
Key words
- Retrovirus
- : An RNA virus copying into DNA.
- Reverse transcriptase
- : The RNA-to-DNA enzyme.
- ELISA
- : The AIDS detection test.
- Contact inhibition
- : Crowding that halts normal growth.
- Benign tumour
- : A confined harmless mass.
- Metastasis
- : Spread seeding new tumours.
- Carcinogen
- : An agent triggering cancer.
Try it in two minutes
- List four HIV routes.
- Track virus to helper-cell fall.
- Split tumours by spread.
Try at home. Explain why touch alone cannot pass HIV.
Substance Abuse
Part of: Say No
Opioids from poppy slow the body, cannabis alters perception, coca stimulant excites through dopamine, and tobacco nicotine raises pressure and heart rate. Curiosity and pressure start use, tolerance demands more, addiction craves while dependence withdraws, and counselling plus healthy pursuits prevent the trap.
Why it matters. Source-effect matching plus stage reasoning covers this section.
Key words
- Opioids
- : Poppy substances slowing body functions.
- Cannabinoids
- : Cannabis chemicals altering perception.
- Coca stimulant
- : Stimulant from coca leaves acting via dopamine.
- Addiction
- : Psychological craving for effects.
- Dependence
- : Body needing doses to avoid withdrawal.
- Withdrawal
- : Illness on abrupt stopping.
Try it in two minutes
- Pair each substance with its plant and effect.
- Split craving from withdrawal.
- Recite five prevention steps.
Try at home. Explain why experimentation slides into dependence.
What your child will practise
- AIDS and Cancer: Ocean Puzzle (Clue Puzzle)
- AIDS and Cancer: Ocean Quick Fire (Quick Fire)
- Body Defences: Jungle Puzzle (Clue Puzzle)
- Common Infectious Diseases: Jungle Quest (Flip and Match)
- Substance Abuse: Desert Quick Fire (Quick Fire)
- Quiz: AIDS and Cancer (8 questions)
- Quiz: Body Defences (8 questions)
- Quiz: Common Infectious Diseases (8 questions)
- Quiz: Substance Abuse (8 questions)